This application is a 371 of PCT/EP01/03277, filed Mar. 22, 2001.
The present invention relates to a process for preparing a 1,3-diol by hydrogenating a feed comprising a 3-hydroxyaldehyde in the presence of a catalyst and a hydrogen source, wherein syngas is used as hydrogen source, and the catalyst is a heterogeneous catalyst comprising copper on a support.
1,3-Diols have plenty of uses, particularly in the synthesis of polymers. For instance, CORTERRA(copyright) polymer is a polyester made of 1,3-propanediol (PDO) and terephthalic acid, which polymer has outstanding properties. Substituted versions of PDO may find similar use. Commercially attractive routes to prepare such 1,3-diols are therefore highly desirable.
One of the more important routes for preparing 1,3-diols involves the hydroformylation of an oxirane, followed by the hydrogenation of the intermediate 3-hydroxyaldehyde. An alternative process involves the hydration of acrolein or higher homologue, again followed by the hydrogenation of the resulting 3-hydroxyaldehyde.
The hydroformylation of oxiranes (epoxides) is described in xe2x80x9cNew Synthesis with Carbon Monoxidexe2x80x9d (Springer-Verlag, 1980), pp. 131-132, and in various patents in the name of Shell (hydroformylation processes have, for instance, been described in EP-A-0478850; and in U.S. Pat. No. 5,463,144; U.S. Pat. No. 5,463,145; U.S. Pat. No. 5,463,146; U.S. Pat. No. 5,527,973; U.S. Pat. No. 5,545,765; U.S. Pat. No. 5,545,766; U.S. Pat. No. 5,545,767; U.S. Pat. No. 5,563,302; U.S. Pat. No. 5,576,471; U.S. Pat. No. 5,585,528; U.S. Pat. No. 5,684,214; U.S. Pat. No. 5,723,389; U.S. Pat. No. 5,770,776; U.S. Pat. No. 5,786,524; U.S. Pat. No. 5,841,003; U.S. Pat. No. 5,945,570; and U.S. Pat. No. 5,986,145).
The conversion of the 3-hydroxyaldehyde is typically carried out by hydrogenation thereof with hydrogen gas in the presence of a homogeneous or heterogeneous catalyst. For instance, hydrogenation of 3-hydroxypropanal (HPA) into 1,3-propanediol (PDO) in the presence of a heterogeneous catalyst is disclosed in WO-A-98/57913 and the prior art described in this reference. This reference also describes the important criteria of a suitable catalyst: high activity and selectivity with a small volume of catalyst, long operational service life, and reasonably priced.
However, many such catalysts lack selectivity and/or stability in slightly acidic environments, and/or in the presence of carbon monoxide. Therefore, a potentially attractive hydrogen source in the form of synthesis gas (xe2x80x9csyngasxe2x80x9d, a blend of H2 and CO) is not used. The present invention aims to provide catalysts that may be used in the preparation of a 1,3-diol by hydrogenation of a 3-hydroxyaldehyde in the presence of syngas as hydrogen source.
As mentioned, 1,3-diols may be the product of a multistep process, wherein syngas is used in a step prior to the hydrogenation, i.e., in the hydroformylation step.
In such processes a catalyst capable of hydrogenating the product of the preceding hydroformylation step in the presence of syngas would be particularly attractive.
It was therefore an aim to provide a process for preparing a 1,3-diol by hydrogenating a feed comprising a 3-hydroxyaldehyde in the presence of a catalyst and a hydrogen source, wherein the catalyst is capable of handling syngas as hydrogen source, and wherein the catalyst meets the aforementioned important criteria.
Accordingly, the present invention provides a process for preparing a 1,3-diol by hydrogenating a feed comprising a 3-hydroxyaldehyde in the presence of a catalyst and a hydrogen source, wherein syngas is used as hydrogen source, and the catalyst is a heterogeneous catalyst comprising copper on a support.
The feed to the process of the present invention preferably comprises the product of an oxirane hydroformylation step, which product comprises a 3-hydroxyaldehyde, a solvent and a homogeneous hydroformylation catalyst. Said homogeneous hydroformylation catalyst preferably comprises a Co-based and/or Rh-based hydroformylation catalyst.
More preferably, a) the oxirane is hydroformylated by reaction with syngas in the presence of a homogeneous hydroformylation catalyst and a solvent, forming a 3-hydroxyaldehyde feed, and (b) the 3-hydroxyaldehyde feed is hydrogenated in the presence of a catalyst comprising copper on a support and syngas as hydrogen source. Preferably, hydroformylation step 1) and hydrogenation step b) are carried out sequentially in connected reactor vessels or in a single reactor vessel.
More preferably, the hydroformylation step a) and the hydrogenation step b) are carried out simultaneously in a single reactor vessel.
The process of the present invention comprises the hydrogenation of feed comprising a 3-hydroxyaldehyde, i.e. a compound of the general formula
R2C(OH)xe2x80x94C(R)2xe2x80x94CH=O
wherein each R independently may be a hydrogen atom or may (jointly) be a hydrocarbon group that is substituted or unsubstituted, and/or aliphatic or aromatic. Each group R may independently vary in size, for instance, from 1 to 20 carbon atoms, preferably from 1 to 10 carbon atoms. In addition, they may bear one or more substituents selected from hydroxy, alkoxy, carbonyl, carboxy, amino, cyano, cyanato, mercapto, phosphino, phosphonyl, and/or silyl groups, and/or one or more halogen atoms. The preferred 3-hydroxyaldehydes are those having in total from 3 to 12 carbon atoms, more preferably from 3 to 8 carbon atoms. The most preferred 3-hydroxyaldehyde is HPA, i.e. wherein each R is a hydrogen atom.
Synthesis gas is a blend of hydrogen and carbon monoxide. It typically is made by partial combustion of a petroleum feed. Commercial syngas comprises hydrogen and carbon monoxide in an H2/CO ratio of about 1.0-2.0. Syngas with a higher H2/CO ratio, e.g., up to about 10.0, and higher, may be prepared by the so-called water gas shift reaction, and such gases may also be used in the process of the present invention. On the other hand, it is an advantage of the present invention that it may cope with carbon monoxide-rich gases, at H2/CO ratios as low as about 0.5. The preferred H2/CO ratio hence varies from about 0.5 to about 10.0, more preferably from about 1.0 to about 5.0.
As indicated, the catalyst comprises copper on a support, which is believed to be at least partially in a metallic state under operating conditions. The catalyst may be a sophisticated catalyst wherein the copper is part of an alloy, and/or wherein the catalyst comprises additional promoter metals. Suitable alloys include metals of Groups 8 to 11 of the Periodic Table. Suitable promoter metals include metals of Groups 1 to 7. However, ordinary catalysts, based on copper as the only active component, have been founds to be quite acceptable.
The nature of the catalyst support is not essential. Suitable supports include inert carriers composed of a clay, a metallic or glass sponge, or based on an inorganic carbide, or oxide, or carbon. For instance, the support may be based on oxides of Group 2-6 and 12-14 metals and mixtures thereof, e.g. ZnO, titania, alumina, zirconia, silica and/or zeolites. Preferred supports are resistant to an acidic medium. Suitable results have been achieved with copper on ZnO, on silica, and on Cr2O3.
The support may be used as fine powder or shaped into mouldings such as, for example, pellets, granules, or extrudates using methods known in the art, such as those described in U.S. Pat. No. 5,364,984. Alternatively, the support may be in the shape of a honeycomb, a foam, a sponge or similarly large monolith.
The amount of copper may also vary widely. For instance, the copper may be present on the support in a quantity of about 0.1 to about 80 w % (% by weight), preferably about 10 to about 50 w %, more preferably about 25 to about 35 w %, relative to the support (i.e., g Cu per 100 g of support).
The synthesis of the copper catalyst is conventional, typically involving the co-precipitation of copper and support precursor. Optionally it can also be prepared by doping a carrier with a copper solution, calcining the loaded carrier, and reducing the same at elevated temperatures under H2. Various supported copper catalyst are commercially available, e.g., for use in the hydrogenation of esters to the corresponding alcohols. Copper containing catalysts are also described in U.S. Pat. No. 5,096,688, which is herein incorporated by reference, in a two-stage process for converting synthesis gas into higher alcohols. This document describes its use for the hydrogenation of undesirable non-alcohol oxygenates and the conversion of water and carbon monoxide in hydrogen gas and carbon monoxide.
The supported copper catalyst may bemused in a continuous process, a semi-continuous process of a batch process. The preferred manner is described in respect of the preferred embodiment disclosed hereinbelow.
The hydrogenation conditions are not very critical. Typically the carbonyl feed is hydrogenated at a temperature ranging from ambient to about 150xc2x0 C., preferably from about 40 to about 80xc2x0 C., and at a pressure ranging from atmospheric to about 15 Mpa (about 150 bar), preferably from about 4 to about 10 Mpa (about 40 to about 100 bar). In the case of continuous processes, liquid hourly space velocities of about 0.1 to about 10 10 hxe2x88x921 are preferred. In batch processes, reaction times varying from about 0.1 to about 10 hours are suitable. Finally, in batch processes, the catalyst may be used in any suitable amount, ranging from about 0.1 to about 50 w %, preferably from about 1.0 to about 10 w %, of catalyst calculated on the weight of the carbonyl compound.
The preferred embodiment comprises the hydrogenation of aqueous HPA solutions, for instance solutions made by the hydroformylation of ethylene oxide (EO) in the presence of a cobalt- or rhodium-based catalyst. In principal, any oxirane may be used, leading to the 3-hydroxyaldehyde mentioned above.
The process of the present invention is particularly beneficial in the multistep preparation of PDO from EO, which ordinarily involves the removal of the hydro-formylation catalyst prior to hydrogenation. Thus, it is known that many cobalt-based catalysts require the presence of carbon monoxide to remain in solution. Since in the xe2x80x9cconventionalxe2x80x9d HPA hydrogenation process only hydrogen gas is present, any remaining catalyst precipitates and pollutes the reactor. In the process of the present invention, such hydroformylation catalysts need no longer be removed prior to the hydrogenation.
Surprisingly, it has been discovered that the copper supported catalyst can hydrogenate HPA with syngas, under conditions that completely poison conventional Group 8-10 metal hydrogenation catalyst. Furthermore, the copper-based catalyst may be present during the hydroformylation of the oxirane, thus substantially reducing the fixed equipment costs. In the most preferred embodiment, this would lead to a xe2x80x9csingle stepxe2x80x9d production of PDO (or similar 1,3-alkanediol) from EO (or corresponding oxirane).
The present invention is illustrated in respect of the hydrogenation of a 3-hydroxyaldehyde (HPA) under syngas, comparing the process of the present invention with that of the prior art using a ruthenium-based catalyst. The present invention is also illustrated in respect of a xe2x80x9csingle stepxe2x80x9d PDO process.